It's actually normal for your ex to begin missing you during this time.
It's possible that they try to contact you. But if they don't, don't be anxious either. After waiting for one month, simply call them and ask them to catch up over coffee. Most probably, the two of you have been up to a lot in one month.
Catching up will also help you assess yourself and check if you still wanna be back together with your ex. So, this is what I recommend for what to do when your ex disregards you. As you take time to focus on yourself, it will be okay if your ex reaches out. Nevertheless, if you still want to see your ex again, call them up in about a month and reawaken that relationship.